1. Field of the Invention
This invention relates to an ink set including a plurality of inks which is stored respectively in ink cartridges having ink storage portions which is brought into a hermetically-closed state, an ink cartridge set, an ink jet recording method, a recording unit and an ink jet recording apparatus.
2. Description of the Related Art
In ink jet recording apparatuses, it is required to supply ink stably from an ink cartridge to a recording head so as not to cause any leakage of the ink from the recording head or any lowering of recording performance because of excess ink supply.
In order to for the ink supply to be stable, it has hitherto been studied to control the pressure of an ink storage portion in the ink cartridge by various methods. For example, a proposal has been made for a method in which water head pressure of the ink is prevented from being applied to the recording head (see Japanese Patent Application Laid-Open No. 2002-234183). In addition, a proposal has been made for an ink storage portion the interior of which is so constituted as to have a porous member as a negative-pressure generating member (see Japanese Patent Applications Laid-Open No. S63-118260, No. H02-000522 and No. H07-060984). A proposal has been further made for use of a pressure plate or a spring member as a negative-pressure generating member (see Japanese Patent Applications Laid-open No. 2003-191489 and No. 2003-251821).
The present inventors have studies the use of an ink cartridge having such an ink storage portion as stated below, as an ink cartridge suited for storing therein an ink containing a pigment as a coloring material (i.e., a pigment ink). Specifically, the inventors have studied the use of an ink cartridge not having any porous ink storing member. It is considered that such an ink cartridge can keep the pigment from sedimentation and that the amount of ink remaining in the ink cartridge after being used up can be reduced to an amount as small as possible. Further, the present inventors have made studies by using as an ink jet recording apparatus an ink jet recording apparatus on which the ink cartridge as stated above can be mounted in plurality.
The present inventors have conducted a so-called cleaning operation in which, when the ink jet recording apparatus is not operated, negative pressure is produced by means of a purging pump communicating with a cap with which ejection orifice lines of the recording head are covered, to discharge any unnecessary ink from ejection orifices by purging. Thereafter, the inventors again operated the apparatus to eject an ink from the recording head. As a result, the inventors have found the following problem to come about. That is, the inventors have found that a phenomenon occurs in which a different ink comes into particular ink channels among the ink channels of a plurality of ejection orifice lines from which the plurality of inks has been discharged by purging through the same cap (this phenomenon is hereinafter referred to as “color mixing phenomenon”).
When the present inventors first observed such a phenomenon, the inventors considered that this color mixing phenomenon was a phenomenon caused by the same mechanism as in the color mixing phenomenon hitherto known in the art. More specifically, the ink adhered to the surface of the recording head or the ink present inside the cap (such ink is hereinafter referred to as “ink residue”) comes into ink channels due to capillary force exerted by the ink channels, so that a different ink comes into the vicinity of ejection orifices of the ink channels. They have considered in this way.
Accordingly, the present inventors have conducted operations in which the ink is ejected inside the cap before the recording is started (this operation is hereinafter referred to as “preliminary ejection”), which is conventionally conducted as a common method for avoiding the color mixing phenomenon. However, the color mixing phenomenon has by no means been resolved even when the number of ink droplets ejected in the preliminary ejection (the number of preliminary ejection droplets) is greatly increased as compared with the number of preliminary ejection droplets that is large enough to resolve the conventional color mixing phenomenon.
Accordingly, the present inventors have conducted the cleaning operation several times for the purpose of discharging all the ink remaining at the part inside the ink channels where the color mixing phenomenon has occurred. However, even though the cleaning operation was performed many times, the color mixing phenomenon was not resolved; instead, a serious degree of the color mixing phenomenon occurred, bringing about a result contrary to their expectations.
On the basis of the results stated above, the present inventors have studied in detail the color mixing phenomenon. As a result, the inventors have found the following. That is, the inventors have found that this color mixing phenomenon involved in the present invention is not the color mixing phenomenon conventionally observed in the vicinity of ejection orifices of ink channels or in the vicinity of ink channels in a common liquid chamber communicating with individual ejection orifices, but a new color mixing phenomenon such that a different ink comes into the insides of ink channels. Herein, the “common liquid chamber” refers to a common liquid chamber communicating, in common, with a plurality of ink channels which communicate respectively with a plurality of ejection orifices in the recording head from which ink is to be ejected. The “insides of ink channels” refer to the whole of the ink channels and common liquid chamber of the recording head and further ink supply paths through which ink is to be fed to the common liquid chamber from the ink storage portion of the ink cartridge.
Further, when the above color mixing phenomenon occurred, the ink jet recording apparatus was left standing for a while after the cleaning operation has been conducted, in the state the ink is not ejected from the recording head. Thereafter, the inventors conducted again recording, where, in the beginning, the recording head ejected the ink that should originally be ejected from the ejection orifices. However, upon continuing the recording in that state for a while, an ink which is not the ink that should originally be ejected from the ejection orifices has suddenly been ejected. It has been found that such a new phenomenon has never been observed occur. Then, the ink which is not the ink that should originally be ejected from the ejection orifices has been found to be the different ink stated above that has come into the insides of ink channels. Further, as the lapsed time has increased during which the recording is not performed after the cleaning operation has been conducted, a phenomenon has occurred in which a different ink that had begun to come into particular ink channels comes into the insides of the ink channels. It has been found that, when such a state is brought about, the matter is far beyond the level of a color mixing phenomenon which can be resolved by somewhat increasing the number of preliminary ejection droplets or by other adjustments.